This study is one of several that uses neuroendocrine challenge studies to investigate the role of 5-HT in psychiatric disorders. MK-212, a phenylpiperazine which is a selective agonist for 5-HT2 receptors, has been the principal agent used for challenges. If cimetidine is shown to be a 5-HT2 agonist similar to MK-212, it may be useful for these challenges.